In recent years, liquid crystal display devices are rapidly becoming popular as alternatives to cathode-ray tubes (CRTs). Such liquid crystal display devices are used in a wide variety of devices, such as television devices, monitors, and mobile phones, because of their characteristics such as energy saving, reduced thickness, and lightweight.
In particular, there has been recently grown the so-called mobile device equipped with (i) a battery functioning as a power supply and having limited capacity and (ii) a liquid crystal display device functioning as display means.
In such a mobile device, the battery having limited capacity is employed as the power supply. Therefore, for a longer continuous operation time of the mobile device, greater importance is placed on reduction of power consumption of the liquid crystal display device.
Under the circumstances, attention has been given to a technique of realizing low power consumption of a liquid crystal display device by (i) increasing an aperture ratio and transmittance of a liquid crystal display panel provided in the liquid crystal display device and (ii) reducing a light amount of a backlight accordingly.
The liquid crystal display device most commonly used in the past is a TN (Twisted Nematic) mode liquid crystal display device which uses liquid crystal molecules having a positive dielectric anisotropy. However, such a TN mode liquid crystal display device has the problem that image quality such as a contrast and a color tone is significantly deteriorated when the liquid crystal display device is viewed at oblique angles from above, from underneath, from the left side, and from the right side, as compared with when viewed from the front.
That is, the TN mode liquid crystal display device has high dependence of image quality on viewing angles, and is therefore not suitable for an application in which the liquid crystal display device is expected to be viewed from a direction other than the front.
An IPS (In-Plane Switching) mode liquid crystal display device and an MVA (Multi-domain Vertical Alignment) mode liquid crystal display device are known as liquid crystal display devices in which such dependence of image quality on viewing angles is improved.
According to the IPS mode liquid crystal display device, dependence of image quality on viewing angles is remarkably improved because orientations of liquid crystal molecules in a plane parallel to a substrate surface are changed in accordance with an applied voltage. However, the IPS mode liquid crystal display device has a problem as follows: that is, two electrodes are provided on a side of a TFT substrate so as to control, for each picture element, liquid crystal molecules in the plane parallel to the substrate surface, and there exist regions above the two electrodes where the liquid crystal molecules cannot be controlled. This leads to a substantial decrease in aperture ratio.
On the other hand, according to the MVA mode liquid crystal display device, at least one of two substrates, between which a liquid crystal layer is interposed, has, on its side contacting the liquid crystal layer, (i) a transparent electrode with protrusions that function as orientation separation means and/or (ii) a transparent electrode with notches that function as orientation separation means. With such a transparent electrode(s), each picture element has regions where the liquid crystal molecules are oriented in respective different directions, and this achieves a wide viewing angle characteristic.
In recent years, however, definition of a liquid crystal display device is getting higher and a size of one (1) picture element tends to be reduced. In such a picture element, there is provided a transparent electrode which is patterned to have protrusions and notches that function as orientation separation means. Under the circumstances, an effective aperture ratio of one (1) picture element tends to be decreased.
In each of picture elements, disorders in orientations of liquid crystal molecules (hereinafter, sometimes referred to simply as “orientation disorder”) are caused in step parts such as edge parts of the picture element, a region where a black matrix is provided, and contact hole sections. In particular, in a case where an effective aperture ratio of one (1) picture element is small as above described, a ratio of an area where orientation disorders occur to a total area of each picture element becomes higher.
As a result, differences in luminance between the picture elements occur due to uneven orientation disorder caused by variations of finished fine patterns (i.e., manufacturing variations). The differences in luminance are viewed as roughness of image, and this leads to a decrease in display quality of the liquid crystal display device.
Considered as a method for suppressing the decrease in display quality due to roughness of image is as follows. That is, (i) a transparent electrode can be employed which is patterned so as to further stabilize orientations of liquid crystal molecules in a region where an orientation disorder occurs; or (ii) a region where roughness of image occurs can be light-shielded.
For example, Patent Literature 1 discloses a vertical alignment type liquid crystal display device which includes picture element electrodes each having a shape formed by three polygonal transparent electrode parts which are connected in series.
FIG. 12 is a view illustrating a schematic configuration of a picture element electrode included in the vertical alignment type liquid crystal display device.
A picture element electrode 348 has a shape formed by three polygonal transparent electrode parts (hereinafter, referred to as “sub-picture-element electrodes 348u”) connected with each other (see FIG. 12). Each picture element electrode 348 is provided in a corresponding sub-picture-element region 349 (see a hatched area in FIG. 12).
Note that each of the sub-picture-element electrodes 348u has a polygonal shape whose outer edge or circumference is substantially equidistant from a center of the sub-picture-element electrode 348u so that liquid crystal molecules are substantially radially oriented above the sub-picture-element electrode 348u. 
The picture element electrodes 348 are provided, in a matrix manner, on an overlayer formed on an active matrix substrate (not illustrated). Each of the picture element electrodes 348 corresponds to any one of colors R (red), G (green), and B (blue), that is, each of the picture element electrodes 348 is provided so as to face any one of color filters 205R, 205G, and 205B (i) which are provided on a counter substrate facing the active matrix substrate and (ii) each of which has a substantially rectangular shape.
As is illustrated in FIG. 12, each of the picture element electrodes 348 has a wire which is a connection section 348c connected to a corresponding one of TFDs (Thin Film Diode) 320. The connection section 348c is made of a material, such as ITO (Indium Tin Oxide), which is identical with that of the picture element electrode 348.
The connection section 348c extends from a circumference of a sub-picture-element electrode 348u, located lowermost in the sub-picture-element region 349, to a contact hole 346. Picture element electrodes 348 belonging to the same column are connected to a single data line 314 in locations of corresponding contact holes 346 via corresponding TFDs 320.
Meanwhile, picture element electrodes 348 belonging to the same row face a single scanning line 214 (depicted by dotted lines in FIG. 12).
Specifically, the scanning lines 214 are provided on the counter substrate, and apertures 214a are formed in each of the scanning lines 214 in locations substantially corresponding to centers of respective sub-picture-element electrodes 348u. When a voltage is applied between the active matrix substrate and the counter substrate, an oblique electric field is caused, in each part where the aperture 214a matches the sub-picture-element electrode 348u, due to an interaction between the aperture 214a and the sub-picture-element electrode 348u. With the configuration, directions in which liquid crystal molecules are tilted are controlled.
As such, it is possible to control the liquid crystal molecules to be radially oriented, in accordance with a voltage to be applied between the active matrix substrate and the counter substrate. This makes it possible to form regions in each of which the liquid crystal molecules are radially oriented.
The overlayer has contact holes 346 each of which is an aperture having a substantially circular shape when viewed from a top of the liquid crystal display device. The connection section 348c of each of the picture element electrodes 348 is electrically connected to the TFD 320 and the data line 314 via the contact hole 346.
In the vertical alignment type liquid crystal display device having such an overlayer configuration, liquid crystal molecules are vertically oriented in an initial orientation state of liquid crystal to which no voltage is being applied. However, liquid crystal molecules located above contact holes are affected by inclined planes of the contact holes having step parts. Therefore, orientation disorders of liquid crystal are caused in the locations above the contact holes.
Under the circumstances, in a case where, for example, the contact holes 346 are provided in an effective display region of the picture element electrode 348, that is, in locations corresponding to the sub-picture-element electrodes 348u or in the vicinity of the locations, liquid crystal molecules in the effective display region are adversely affected by orientation disorders of liquid crystal molecules caused in locations corresponding to the contact holes 346, and accordingly an image quality problem, such as display unevenness, is caused.
According to the configuration disclosed in Patent Literature 1, in order to suppress occurrence of such an image quality problem, each of the contact holes 346 is provided in a location which is in a picture element region but does not match any of the picture element electrodes 348 in the sub-picture-element region 349 (see FIG. 12). Specifically, each of the contact holes 346 is provided in a location farthest from the picture element electrode 348 in the sub-picture-element region 349 (i.e., at a corner of the sub-picture-element region 349).
According to the configuration, it is possible to cause the contact hole 346 to be distant from the sub-picture-element electrode 348u (corresponding to the effective display region) as far as possible. Therefore, liquid crystal molecules in the effective display region, which corresponds to locations of the sub-picture-element electrodes 348u and serves as a display section, are hardly affected by the orientation disorders caused in the locations of the contact holes 346.
Patent Literature 1 describes that, with such a configuration, it is possible to realize a liquid crystal display device which can (i) suppress occurrence of an orientation disorder of liquid crystal molecules caused in the effective display region and (ii) display an image with high quality.
Patent Literature 1 further describes that, since the contact hole 346 is provided in the location which does not match the picture element electrode 348, it is possible to prevent a decrease in aperture ratio.